With the extension of the borehole in the drilling process, the rocks need to be continuously broken, and usually for a distance of several kilometers. However, with the increase of the well depth, the difficulty of rock breaking increases while the efficiency of rock breaking decreases. The conventional rock breaking methods mainly include the mechanical method and the jet hydraulic one, and the latter requires very high jet pressure.
Under the current drilling conditions, the jet only has an auxiliary function of hydraulic rock breaking. When the jet pressure is increasing, the effect of hydraulic auxiliary rock breaking will be improved, and even rocks may be directly broken in a hydraulic manner. In order to directly break rocks in a hydraulic manner, the jet pressure shall exceed the threshold pressure of rock breaking. There are two methods for increasing the drilling fluid pressure. One method uses the surface supercharging, which improves the downhole jet velocity by increasing the volume of the surface pumped high pressure drilling fluid. But practices have shown that this method is unfeasible due to low efficiency, high cost and insecurity. Since the impulse jet usually has a stronger rock breaking capability than the conventional continuous jet under the same pressure, another underground supercharging method has been proposed. Although various underground superchargers emerges in china and other countries, they all have certain defects, such as complex structure, low reliability, low efficiency, or the supercharging is not enough. For example, the Chinese patent No. 93116601.2 discloses an “automatic supercharging device”, which controls the direction change and activates supercharge by using a combination of the motor pilot valve and the hydraulic changeover valve. However, the defects of the device include challenges in direction control and short seal life. The Chinese patent No. 200520103214.8 discloses a “fluid supercharger”, which supercharges by using an underground plunger, while the seal life is always not well prolonged and the supercharging effect is poor. The Chinese patent No. 200820019505.2 discloses “underground booster pump using positive displacement motor with double helical grooves”, which uses a positive displacement motor to drive a plunger to change directions through the double helical grooves, but the fluid passage is too small due to the large volume of the helical grooves, thus the erosion is serious. The Chinese patent No. 201020125587.2 discloses an “underground drill string damping and supercharging device”, which uses a spring controlled valve to implement reciprocating supercharging, but the spring does cannot guarantee working stably and reliably enough underground, and the supercharged value will be decreased. Therefore, a new underground supercharging device needs to be developed to implement the underground supercharging.
In view of the above defects of the prior art, the inventors develop an impulse-type underground supercharged jet drilling method and device of the present invention based on their years of production and design experiences in related fields for many years, which combines the advantages of both impulse jet drilling and ultrahigh jet drilling, and can greatly improve rock breaking efficiency and drilling speed.